[Discuss] SSD drives vs. Mechanical drives

[bogstad at pobox.com (Bill Bogstad)]

On Tue, May 6, 2014 at 7:29 AM, Edward Ned Harvey (blu)
<blu at nedharvey.com> wrote:
>
>
> Truth is:  Hardware mirroring doesn't provide data integrity.  But software mirroring with btrfs/zfs do indeed provide data integrity.

For purposes of this email:

data loss: you don't get any data
data integrity: you get data, but it isn't what you wrote to the storage system

Mirroring will help prevent data loss, but not help with data integrity.
(Unless you read both copies and compare at which point you
have converted a data integrity event into a possible data loss event).

RAID involving checksums can help with data integrity, but only between
were the checksum is generated and the data's final resting place.   And only if
the system bothers to verify the checksums on reads when the downstream devices
don't report an error.   Depending on precisely how your RAID works it
might not bother to do so for performance reasons.    I don't know how common
this issue, but it is certainly possible.   ZFS or similar filesystems
which specifically say that
they are doing so cover more of the data path with a data integrity guarantee.

Bill Bogstad